Although flight control cable continuity could not be established, nothing was found that would indicate any faults with the flight controls before impact. Propellor blade marks and damage indicated that the engine was producing considerable power on impact. Calculations indicate that density altitude effects would have reduced the aircraft's performance, compared to its performance on a standard day. Post-accident calculations showed that the aircraft weighed at least 5350pounds, about 250pounds over its maximum allowable take-off weight. The actual weight of the aircraft was likely even greater, as some of the cargo was destroyed by fire or was unrecoverable. The overweight condition would have had the effect of further reducing the aircraft's performance and may have been a factor in the aircraft not out-climbing the rising terrain. Tree damage and contact markings indicate the aircraft was in a wings-level, climbing attitude when it struck tree tops. The aircraft was approaching rising terrain head-on and very close to the summit. A principle of mountain flying is that a pilot should approach a saddle at a 45-degree angle, so there will be room to turn away if it becomes obvious the aircraft will not clear the high terrain. It could not be determined why the pilot did not approach at a 45-degree angle and then simply turn away from the rising terrain when contact with the tree tops became imminent.Analysis Although flight control cable continuity could not be established, nothing was found that would indicate any faults with the flight controls before impact. Propellor blade marks and damage indicated that the engine was producing considerable power on impact. Calculations indicate that density altitude effects would have reduced the aircraft's performance, compared to its performance on a standard day. Post-accident calculations showed that the aircraft weighed at least 5350pounds, about 250pounds over its maximum allowable take-off weight. The actual weight of the aircraft was likely even greater, as some of the cargo was destroyed by fire or was unrecoverable. The overweight condition would have had the effect of further reducing the aircraft's performance and may have been a factor in the aircraft not out-climbing the rising terrain. Tree damage and contact markings indicate the aircraft was in a wings-level, climbing attitude when it struck tree tops. The aircraft was approaching rising terrain head-on and very close to the summit. A principle of mountain flying is that a pilot should approach a saddle at a 45-degree angle, so there will be room to turn away if it becomes obvious the aircraft will not clear the high terrain. It could not be determined why the pilot did not approach at a 45-degree angle and then simply turn away from the rising terrain when contact with the tree tops became imminent. As the aircraft approached high terrain in a climb, the pilot, for undetermined reasons, did not turn away from the terrain; the aircraft struck tree tops and crashed. The aircraft's climb performance was adversely affected by density altitude and the relatively high aircraft weight, so that the aircraft was unable to clear the high terrain ahead.Findings as to Causes and Contributing Factors As the aircraft approached high terrain in a climb, the pilot, for undetermined reasons, did not turn away from the terrain; the aircraft struck tree tops and crashed. The aircraft's climb performance was adversely affected by density altitude and the relatively high aircraft weight, so that the aircraft was unable to clear the high terrain ahead. The licenced passenger had not informed the TC medical examiner who conducted her last medical that she had been diagnosed with coronary artery disease, posing the risk that she could pilot an aircraft while not medically fit to do so. The aircraft was being operated at a higher weight than was justified by the STC, under which it was converted to an amphibian. Some of the structural modifications called for by the STC for the higher weight had not been carried out.Findings as to Risk The licenced passenger had not informed the TC medical examiner who conducted her last medical that she had been diagnosed with coronary artery disease, posing the risk that she could pilot an aircraft while not medically fit to do so. The aircraft was being operated at a higher weight than was justified by the STC, under which it was converted to an amphibian. Some of the structural modifications called for by the STC for the higher weight had not been carried out. It could not be determined who was piloting the aircraft on the occurrence flight.Other Findings It could not be determined who was piloting the aircraft on the occurrence flight.